126 
minor importance which we cannot discuss here. 
These, however, do not interfere with the facts 
of general agreement ; and there is great proba- 
bility that the shell-covered forms of all kinds 
which have the protoconch — namely, the an- 
cient and modern Gastropoda, Tentaculites, 
and the ancient Pteropoda, and all the radical 
forms of Cephalopoda — had a com- 
mon origin, probably in some cham- ~ 
berless and septaless form similar 
to the protoconch. Von Ihering 
has already designated this proto- 
type as probably Tentaculites. No 
exact correspondent to the proto- 
conch is yet known to us; but cer- 
tainly Tentaculites is nearer to the 
protoconch of both Cephalopoda 
and Gastropoda than any other 
known ancient form. 
The young of the simplest and 
earliest of Ammonoidea, the Nau- 
tilini, have in varieties of two spe- 
cies, as shown by Barrande, a 
straight apex, like the adult shell 
of Orthoceras, the radical of the 
Nautiloidea. We have already 
claimed that this fact was sufficient 
to prove the high probability of a 
common origin from a _ straight 
shell like Orthoceras for both of 
these orders; and we are now able 
to reiterate this conclusion, and to 
meet the objections of the great 
paleontologist Barrande, and _ his 
supporters, more effectually than 
ever before. 
Goniatites compressus, sp. Bey- 
rich (Sand. verst. Nassau, pl. 11, 
fig. 4), is a shell which differs from 
all other Ammonoidea in an essen- 
tial and highly important charac- 
ter. The septa have no inner lobe. 
The v-shaped annular lobe which 
occurs in all the Ammonoidea ex- 
cept the Nautilini is also absent in 
this species. What is more to the 
point, this shell has the sutures of 
a true nautiloid, since it has the 
dorsal saddle, in place of the dor- 
sal lobe, of the sutures of its near- 
est allies, the Nautilini, and all of the re- 
maining Ammonoidea. Goniatites ambigena 
Barr., of the Silurian, is a close ally of this 
Devonian species, and the two are the only 
Ammonoidea which are not truly nautilian in 
form. The whorls are in contact; but there 
is no impressed zone, and no sutural lobes 
on the dorsum, as in true nautilian shells. On 
SCIENCE. 
~ acter of the septa in later Ammonoidea. 
EG 
Fie. 1.— Aspect of the apex of the conch in Orth. unguis Phill., after the proto- 
conch has been shed in the usual manner. 
c, cicatrix. 
Fie. 2.— Aspect of the apex, after the protoconch has been accidentally broken 
off, fracturing the outer shell, and exposing the cicatrix. 
Fies. 3-5.— Apex and protoconch of Orth. elegans Munst. from the front, side, 
and above. 
Fries. 6, 7.— Another individual, said to be of the same species, less magnified. 
a b, as before. 
outer shell on the protoconch itself, showing the continuity of the shell over 
this part (a), and completing the evidence that it must have been the shell 
which enclosed the embryo, and could not have been a mere plug, as asserted 
by Barrande (Syst. sil., pl. 488). 
whet 4 
the contrary, they are purely gyroceran forms, 
with rounded dorsum and sutural saddles in 
place of lobes. All of the Nautilini and G. 
compressus also have the septa concave, as in 
the Nautiloidea, in place of the convex char- 
As 
doubts may disturb the mind as to whether G. 
sil 
b, conch or shell of the apex; 
6 c, as before. 
a, protoconch; 0, shell of apex. 
The author has also, in other species, traced the striae of the 
compressus is an ammonoid at all, we recom- 
mend a comparison of this shell with the young 
of Goniatites fecundus of Barrande, which is 
a miniature copy made by heredity. 
Bactrites is a perfectly straight form, simi- 
lar to these Goniatites in very important char-_ 
acteristics, especially the siphon and septa. 
This same genus includes straight cones like 
[Vox. III., No. 52. 
fs 
